One Cold Cylinder - 930 Race car

[Adam144]

Hoping someone here can help, my dad and I have been reading around and troubleshooting constantly.

We're having a problem with his 1980 Porsche 930 race car. It's a factory 930 3.3L with CIS and an MSD ignition system (6AL with Blaster coil).

We had a problem at a recent HPDE where it ran fine for a few laps and then all of the sudden it would cough and sputter (often dying off and then firing right back up) and would never come out of this underpowered coughing fit.

The front-most passenger side cylinder (#6?) spark plug is wet/black (running way too rich). Since this happened dad made brand new Taylor wires and re-built the distributor, this didn't stop the problem. The biggest indicator is the temperature reading with an infra-red thermometer on the #6 cylinder is almost 200 deg F cooler than the other 5, it registers 250 deg F where the others read around 450 consistently. A compression test revealed that it is well within range and consistent with the other cylinders.

This leads me to believe there is something wrong with the CIS? I think there's something wrong with the fuel distributor where the supply for cyl #6 is stuck open and feeding it way too much fuel constantly? Both fuel pumps are running and we're running out of ideas. Any input?

[gsxrken]

You might have a bad injector. Have you checked their spray patterns? Another test is to pull all the injectors and put them each in glass jars and conduct a volume comparison test by running the pumps for a short time.
Of course a cracked plug can drive you nuts too, but I assume new plugs went in with new wires.

[Adam144]

Originally Posted by gsxrken

You might have a bad injector. Have you checked their spray patterns? Another test is to pull all the injectors and put them each in glass jars and conduct a volume comparison test by running the pumps for a short time.
Of course a cracked plug can drive you nuts too, but I assume new plugs went in with new wires.

Yes new plugs went in along with the wires, old plugs check out fine.

We did try a new injector before during the track day to no avail. Are we right in our thinking that it could be the fuel distributor? Does it work in such a way that it could feed more fuel constantly into one cylinder? That's the only reason I can think it would run cooler. Either no spark (which we've ruled out) or too much fuel. If it was not enough fuel it would lean the cylinder out and run hot.

Really frustrating and a lot of time into this so far. Two weeks until the next HPDE.

[Ronnie's.930]

Information in this thread might help -

CIS injector flow testing

[EmptyGarage]

If its compatible, I have a fuel distributor from an 86 turbo that i can send you to try. Let me know if you interested. Shipped from Nova Scotia so it could be there in a few days.

[Adam144]

Originally Posted by Ronnie's.930

Information in this thread might help -

CIS injector flow testing

Had heard of doing this but thank you for the "How-to" walkthrough, that helps greatly. We're going to check the spray patterns and volumes tonight.

[Adam144]

Originally Posted by EmptyGarage

If its compatible, I have a fuel distributor from an 86 turbo that i can send you to try.

Wow, thanks! We will see where we are at tonight with the jar filling. I will keep it in mind though, I appreciate the help.

[Adam144]

I suppose I should also mention that the fuel distributor was sent to Imagine Auto to be re-worked (I assume for higher flow?) by one of the previous owners according to the paperwork with the car.